This invention relates to a tool intended for chip removing machining the tool being of the type that comprises a shaft, which at a front end has a cutting body made of a hard material, which is connected detachably to the shaft by means of a drawbar arranged in a bore inside the shaft. The drawbar, at a front end thereof, has a locking device for mechanical engagement with the cutting body and which is movable axially between a protruded position and a retracted position by means of a tightening element located at a distance from the locking device.
Cutting tools of the type that makes use of a cutting body detachable from a shaft may, in practice, be in the form of milling cutters, in particular shank-type cutters, drills or thread cutters, the shaft usually having a long narrow, cylindrical shape. In modern machine tools, said shafts are so sophisticated and expensive that they cannot, for economical reasons, be integrated with the wearing part of the tool, viz. the cutting body, while forming a single tool which may be discarded when the cutting body has been consumed. In other words, it is profitable to make the cutting body proper as a detachable unit, which may be replaced, while the expensive shaft may be used during a long period of time. A certain category of such tools (see e.g., U.S. Pat. No. 5,607,263 and German Document 34 48 086) is based on the cutting body being fastened at the front end of the shaft by means of a short screw, which via a through hole in the cutting body is fastened in a female screw thread which opens up at the front end of the shaft. An aggravating disadvantage of this type of tool is, however, that cutting edges cannot be formed in the area of the front end of the hole formed in the cutting body, from which it follows that the cutting body may be formed only for milling (e.g. milling of T-grooves), but not for drilling.
Another category of tools, to which the invention relates, uses a drawbar of the type mentioned initially in order to connect, detachably, the cutting body to the shaft. The front end of the drawbar may then be inserted from behind in the cutting body and by means of a locking device be brought into mechanical engagement with the cutting body. In this way, the front end of the cutting body will not be intersected by any holes, and therefore cutting edges for drilling purposes or full radius edges for milling purposes may be formed on the front end of the cutting body. A tool employing a drawbar of this type has been described in EP 0 911 101. In this known tool, a drawbar extends through a through-bore inside the tool shaft and is connected, at a rear end, to a nut by means of which the bar may be displaced axially inside the shaft between a protruding position, in which the cutting body may be connected to the front end of the drawbar, and a withdrawn position in which the cutting body is clamped against the front end of the shaft, more precisely by means of a locking device at the front end of the drawbar.
However, in this known tool, the locking between the cutting body and the shaft is unreliable. That is, the locking device consists of a ring-like bulge formed on the front end of the drawbar which interacts with an inner, cone-shaped surface on a neck protruding from the shaft, which in turn is inserted into a rearwardly open, cylindrical space in the cutting body, said neck expanding when the ringlike bulge of the drawbar is pulled therein; all while achieving a friction locking between the inside of said cylinder space and the outside of said neck. If a tool of this type is exposed to considerable cutting forces, there is, however, a risk of the cutting head coming loose from the shaft or displaced from a centered position thereon.
The present invention aims at obviating the above-mentioned inconveniences of the prior art and at providing an improved tool of the type mentioned initially. Thus, a primary aim of the invention is to provide a tool, the cutting body of which may be corrected to an appurtenant shaft in an accurate and reliable way. Another aim of the invention is to create a tool, which enables assembly and disassembly of the cutting body in a fast and simple way while ensuring an exact centering or positional determination of the cutting body in relation to the shaft. It is also an aim to provide a tool, which is structurally simple and may be manufactured by means of conventional manufacturing methods.
According to the invention, at least the primary aim is attained by a tool for chip removing machining which comprises a shaft having a front end and a bore extending through the shaft and the front end. A cutting body, formed of a harder material than the shaft, is removably disposed at the front end of the shaft. The cutting body includes a rear end facing the front end of the shaft, and a cavity formed in the cutting body. The rear end of the cutting body includes an opening which communicates with the cavity. The opening has a smaller cross-section than the cavity. A drawbar is arranged in the bore of the shaft. The drawbar includes a front end sized to pass through the opening. The front end of the drawbar has a locking device removably disposed within the cavity. The locking device is sized to bear against an interior rear surface of the cavity to prevent removal of the cutting head from the drawbar. An actuating element is operably connected to the drawbar for moving the drawbar axially along the bore for selectively moving the rear end of the cutting body into and out of engagement with the front end of the shaft.